Abstract
The adherence of underwater air bubbles to surfaces is a serious cause of malfunction in applications such as microfluidics, transport, and space devices. However, realizing spontaneous and additional unpowered transport of underwater air bubbles inside tubes remains challenging. Although superhydrophilic polydimethylsiloxane (PDMS) tubes are attracting attention as air bubble repellents, superhydrophilic PDMS, which is fabricated via oxygen plasma treatment, has a disadvantage in that it is weak against aging. Here, we present a tube with the ability to self-remove air bubbles, which overcomes the drawback of rapid aging. PDMS containing Silwet L-77 with a hierarchical nano-microstructure exhibiting subaqueous aerophobicity was fabricated. We conducted adherence and saturation experiments of air bubbles using the fabricated PDMS tube with Silwet L-77 to investigate the mechanism of bubbles adhering to and separating from the fabricated tube surface. The developed PDMS with Silwet L-77 exhibits a strong self-removal effect with an air bubble removal of 97.7%. The adherence and saturation experiments suggest that the transparent superhydrophilic-underwater aerophobic PDMS is a potentially exceptional tool for spontaneously separating air bubbles attached to tube surfaces.